1. Field of the Invention
The subject matter described herein relates generally to devices and methods for volumetric imaging and, more particularly, to devices and methods for processing volumetric images.
2. Related Art
Image registration involves the correlation of coordinate systems between multiple volumetric images of an object. For example, pre-operative imagery may be correlated to intra-operative, near real time, imagery in order to provide a complete global data set of an object for use by a surgeon operating with surgical equipment such as that sold under the mark “INNOVA” by the General Electric Company of Fairfield, Conn. The global data set that the pre-operative volumetric imaging provides, may be necessary as the intra-operative imagery images a much smaller region than the pre-operative imagery. For example, a pre-operative full abdomen scan may be registered with an intra-operative scan of an intervention site such as that of the liver or heart.
In one example of a current method of image registration, U.S. Patent Publication No. 2006/0002631 to Fu et al describes a method for image registration between a pre-operative three dimensional image and a two dimensional inter-operative image. This is accomplished by creating digital reconstructed radiographs from the three dimensional images and using a similarity measure (to compensate for local motion, position or deformation) to compare pixel intensities in the two dimensional image with that in the digital reconstructed radiographs. Image registration may be performed in a selected region of interest, which is based on defining an entropy measure H thereof and then selecting the region within the image in which the entropy measure is maximized.
However, disadvantages arise with use of such pixel intensity measuring and comparing methods in that the similarity metrics used depend on the overlapping region. They are not defined for images that do not overlap. Instead, each will either likely produce a poor result or will require several iterations to converge. For example, there might be several local minima where a purely intensity based registration might converge.
It will be noted that the publication entitled “Intelligent Data Splitting for Volume Data”; Shen and Bartsh, SPIE Medical imaging 2006 describes a method of volume splitting which includes creating a topogram and other forms of one-dimensional profiles. However, a disadvantage to this method is that it requires manual intervention when the pre-operative and intra-operative datasets have low overlap. In such a situation the user is required to manually provide point-pair correspondence, which it will be appreciated, can be fairly time-consuming and may even be unacceptable in a surgical environment. Other traditional atlases and roadmaps rely on detailed segmentation of structures that also can be time consuming and restricted to a local anatomy or dependent on data type or modality.
Accordingly, to date, no suitable device or method of identifying an ROI in a particular image scan, or providing registration between image scans within a reasonable short period of time, is available.